Error detection and rejection for a diagnostic testing system

ABSTRACT

A system for measuring a property of a sample is provided. The system comprises a diagnostic measuring device having a memory and a diagnostic test strip for collecting the sample. The strip has embedded thereon a pattern representative of at least first data and second data, the first data being data representing at least one of parameters related to measuring the property, codes usable for calibration of the diagnostic measuring device, or parameters indicating proper connection between the measuring device and the test strip and the second data usable for detecting and rejecting potential errors affecting the proper measurement of the property.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/683,484, filed on Apr. 10, 2015 which is acontinuation application of U.S. patent application Ser. No. 11/734,473,filed on Apr. 12, 2007, now U.S. Pat. No. 9,029,157, each of which areincorporated herein by reference in their entireties.

FIELD

The present invention relates to error detection and rejection insystems and methods which electrochemically sense a particularconstituent within a fluid through the use of diagnostic test strips.

BACKGROUND

Many industries have a commercial need to monitor the concentration ofparticular constituents in a fluid. In the health care field,individuals with diabetes, for example, have a need to monitor aparticular constituent within their bodily fluids. A number of systemsare available that allow people to test a body fluid, such as, blood,urine, or saliva, to conveniently monitor the level of a particularfluid constituent, such as, for example, cholesterol, proteins, andglucose. Individuals with diabetes, a pancreatic disorder characterizedby insufficient insulin production, prevents the proper digestion ofglucose, have a need to carefully monitor their blood glucose levels ona daily basis. A number of systems that allow people to convenientlymonitor their blood glucose levels are available. Such systems typicallyinclude a test strip where the user applies a blood sample and a meterthat “reads” the test strip to determine the glucose level in the bloodsample.

Among the various technologies available for measuring blood glucoselevels, electrochemical technologies are particularly desirable becauseonly a very small blood sample may be needed to perform the measurement.In amperometric electrochemical-based systems, the test strip typicallyincludes a sample chamber that contains reagents, such as glucoseoxidase and a mediator, and electrodes. When the user applies a bloodsample to the sample chamber, the reagents react with the glucose, andthe meter applies a voltage to the electrodes to cause a redox reaction.The meter measures the resulting current and calculates the glucoselevel based on the current. Other systems based on coulometry orvoltametry are also known.

Because the test strip includes a biological reagent, every stripmanufactured is not reproducible with the exact same sensitivity.Therefore, test strips are manufactured in distinct lots and dataparticular to that lot is often used as a signal by the meter'smicroprocessor to assist in accurately performing the meter calculation.The data is used to help accurately correlate the measured current withthe actual glucose concentration. For example, the data could representa numeric code that “signals” the meter's microprocessor to access andutilize a specific set of stored calibration values from an on-boardmemory device during calculation.

In past systems, the code particular to a specific lot of strips hasbeen input into the meter manually by the user, or connected throughsome type of memory device (such as a ROM chip) packaged along with teststrips from a single manufacturing lot. This step of manual input, orconnection by the user, adds to the risk of improperly inputting thewrong code data. Such errors can lead to inaccurate measurements and animproper recording of the patients history. Past systems have alsoincluded bar-code readable information incorporated onto individualstrips. Individually imprinting a particular bar-code on each strip addssignificant manufacturing costs to the strip production and requires theadditional expense of a bar-code reader incorporated within the meter inorder to obtain the information.

It should be emphasized that accurate measurements of concentrationlevels in a body fluid, such as blood, may be critical to the long-termhealth of many users. As a result, there is a need for a high level ofreliability in the meters and test strips used to measure concentrationlevels in fluids. Thus, it is desirable to have a cost effectiveauto-calibration system for diagnostic test strips that more reliablyand more accurately provides a signaling code for individual teststrips.

Embedding strip lot calibration information onto individual test stripswhich is readable by the instrument (meter), eliminates the need for theuser to match the meter's lot calibration to the vial of strips. Nolonger needing to rely on the user to properly calibrate the meter's lotcode removes the possibility of user error for this critical step.

Although user technique error is eliminated from automaticallycalibrated systems, the system is still subject to potential instrumentread errors due to normal variations in production of strips andinstruments. These systems are susceptible to erroneously readcalibration codes whether the lot code is embedded electrically,mechanically, optically or otherwise. Abating or at least reducing thechance for a instrument read error will greatly enhance the reliabilityof the system.

Complete elimination of read error is possible, but is limited by thenumber of useful data bits that can be encoded on the small stripstructure. Minimizing read errors is possible without sacrificing thenumber of available data bits for auto-calibration, but requires propermathematical arrangement of and numbering of lot codes. A combination ofthe techniques taught in the invention described below can be employedto vary the read error rejection up to 100%, depending on apredetermined acceptable level of error rejection.

On-strip coding is a relatively new concept in glucose testing, whichhas the potential to greatly improve the accuracy of glucose readings.Systems that do not protect against test strip coding errors, eitherthrough detecting and rejecting strips which contain errors, orcorrecting read errors, will be subject to suboptimal performance andmay produce inaccurate glucose readings.

SUMMARY

Embodiments of the present invention are directed to a system formeasuring a property of a sample, a method for determining a constituentlevel within a fluid, and a method for encoding a code comprising aplurality of bits on a diagnostic test strip for determining aconstituent level within a fluid comprising, such that impacts ofpossible bit errors are minimized that obviate one or more of thelimitations and disadvantages of prior devices and methods.

One embodiment consistent with the present invention is directed to asystem for measuring a property of a sample, comprising a diagnostictest strip for collecting the sample, the strip having informationembedded thereon; a diagnostic measuring device for receiving the teststrip, reading the embedded information, and measuring the sample; andthe diagnostic device further comprising an error detection routine fordetecting errors reading the embedded information.

Another embodiment consistent with the present invention is directed toa system for measuring a property of a sample, comprising a diagnosticmeasuring device having a memory; a diagnostic test strip for collectingthe sample, the strip having a conductive pattern embedded thereon, theconductive pattern being representative of at least first data andsecond data, wherein the first data being data representing at least oneof parameters related to measuring the property, codes usable forcalibration of the diagnostic measuring device, or parameters indicatingproper connection between the measuring device and the test strip; andthe second data usable for detecting and rejecting potential errorsaffecting the proper measurement of the property.

Another embodiment consistent with the present invention is directed toa method of determining a constituent level within a fluid comprisingproviding a diagnostic test meter, the test meter comprising a memoryand a processor; providing a diagnostic test strip, the test stripcomprising at least one code embedded thereon; inserting the test stripinto the test meter, the test meter reading the at least one code;performing an error detection and rejection algorithm on the at leastone code; and determining the constituent level of the fluid if theerror detection and rejection algorithm does not detect an error.

Another embodiment consistent with the present invention provides amethod for minimizing the impact of potential errors that may occur whena device reads a diagnostic test strip including a first code comprisinga plurality of bits arranged in a physical arrangement, the comprising:determining a probability of each bit to cause a read error;constructing a logical arrangement of the bits different than thephysical arrangement based on the probability, wherein the logicalarrangement comprises the bits arranged such that the impact ofpotential read errors is minimized.

Additional features and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Thefeatures and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general cross-sectional view of a test strip according to anembodiment of the present invention.

FIG. 2 is a top perspective view of a test strip inserted within a meterstrip connector according to an embodiment of the present invention.

FIG. 3 is a general cross-sectional view of a test strip inserted withina meter strip connector according to an embodiment of the presentinvention.

FIG. 4 is a top view of a distal portion of a test strip illustrating adistal strip contact region, consistent with an embodiment of thepresent invention.

FIG. 5 illustrates a meter strip connector receiving a distal stripcontact region of test strip consistent with the present invention.

FIG. 6 illustrates an test strip having a sample code embedded thereon,consistent with the present invention.

FIG. 7 is a schematic circuit representation of the meter stripconnector and the meter micro-controller operating in a digital mode,consistent with the present invention.

FIG. 8 is a flowchart illustrating a method for performing errordetection and rejection using a trending algorithm, consistent with thepresent invention.

FIG. 9 is a flowchart illustrating a method for performing errordetection and rejection using a checksum algorithm which computes themodulus of bits in a code, consistent with the present invention.

FIG. 10 is a flowchart illustrating a method for performing errordetection and rejection using a redundant code, consistent with thepresent invention.

FIG. 11 is a flowchart illustrating a method for performing errordetection and rejection using a method of selectively reducing thenumber of available codes, consistent with the present invention.

FIG. 12 provides Table 2, which shows the results of Table 1 using anerror grid.

FIG. 13 is a flowchart for illustrating a method for constructing alogical arrangement consistent with an embodiment of the presentinvention.

DETAILED DESCRIPTION

Reference will now be made in detail to the present embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

According to exemplary embodiments, the invention relates to a systemfor measuring a body fluid constituent which includes a test strip and ameter, and detecting, rejecting, and minimizing any errors that mayoccur. An individual test strip may also include an embedded coderelating to data associated with test strips belonging to a particularlot, data particular to that individual strip, and preferably dataassociated with detecting, rejecting and minimizing errors. The embeddedinformation presents data readable by the meter signaling the meter'smicroprocessor to access and utilize a specific set of calibrationparameters stored in a memory particular to test strips from amanufacturing lot to which the individual strip belongs, or to anindividual test strip. The embedded information further includes datareadable by the meter relating to detecting, rejecting, or correctingany errors. For purposes of this disclosure, “distal” refers to theportion of a test strip further from the device operator during normaluse and “proximal” refers to the portion closer to the device operatorduring normal use.

The test strip may include a sample chamber for receiving a user's fluidsample, such as, for example, a blood sample. The sample chamber andtest strip of the present specification can be formed using materialsand methods described in commonly owned U.S. Pat. No. 6,743,635, whichis hereby incorporated by reference in its entirety. Accordingly, thesample chamber may include a first opening in the proximal end of thetest strip and a second opening for venting the sample chamber. Thesample chamber may be dimensioned so as to be able to draw the bloodsample in through the first opening, and to hold the blood sample in thesample chamber, by capillary action. The test strip can include atapered section that is narrowest at the proximal end, or can includeother indicia in order to make it easier for the user to locate thefirst opening and apply the blood sample. The meter and test strip maybe such as described in U.S. patent application Ser. No. 11/181,778,which is hereby incorporated by reference in its entirety, and describedbelow.

A working electrode and counter electrode can be disposed in the samplechamber optionally along with fill-detect electrodes. A reagent layer isdisposed in the sample chamber and preferably contacts at least theworking electrode. The reagent layer may include an enzyme, such asglucose oxidase, and a mediator, such as potassium ferricyanide orruthenium hexamine. The test strip has, near its distal end, a firstplurality of electrical strip contacts that are electrically connectedto the electrodes via conductive traces. In addition, the test strip mayalso include a second plurality of electrical strip contacts near thedistal end of the strip. The second plurality of electrical contacts canbe arranged such that they provide, when the strip is inserted into themeter, a distinctly discernable lot code readable by the meter. As notedabove, the readable code can be read as a signal to access data, such ascalibration coefficients, from an on-board memory unit in the meterrelated to test strips from that lot, or even information correspondingto individual test strips, and preferably information relating todetecting, rejecting, or correcting possible errors.

The meter may be battery powered and may stay in a low-power sleep modewhen not in use in order to save power. When the test strip is insertedinto the meter, the first and second plurality of electrical contacts onthe test strip contact corresponding electrical contacts in the meter.The second plurality of electrical contacts may bridge a pair ofelectrical contacts in the meter, causing a current to flow through aportion of a second plurality of electrical contacts. The current flowthrough the second plurality of electrical contacts causes the meter towake up and enter an active mode. The meter also reads the codeinformation provided by the second plurality of electrical contacts andcan then identify, for example, the particular test to be performed, ora confirmation of proper operating status or the type of errordetection, rejection, or correction method, algorithm, or routine beingapplied. In addition, the meter can also identify the inserted strip aseither a test strip or a check strip based on the particular codeinformation. If the meter detects a check strip, it performs a checkstrip sequence. If the meter detects a test strip, it performs a teststrip sequence. Moreover, the meter can perform a error detection, errorrejection, or error correction routine based on the code information.Consistent with an embodiment of the present invention the meter mayhave an internal memory therein, which can store microprocessoralgorithms for performing calibrations, or an error detection,rejection, or correction method, routine, or algorithm. The internalmemory within the meter may also store a firmware, which containsinstructions for performing a stored microprocessor algorithm, an errordetection, rejection, or correction method, routine, or algorithm, andinstructions for the general operation of the meter. Moreover,consistent with an embodiment of the present invention, the firmware maybe upgradeable, allowing for additional or alternative instructions tobe stored in the internal memory.

In the test strip sequence, the meter validates the working electrode,counter electrode, and, if included, the fill-detect electrodes, byconfirming that there are no low-impedance paths between any of theseelectrodes. If the electrodes are valid, the meter indicates to the userthat sample may be applied to the test strip. The meter then applies adrop-detect voltage between the working and counter electrodes anddetects a fluid sample, for example, a blood sample, by detecting acurrent flow between the working and counter electrodes (i.e., a currentflow through the blood sample as it bridges the working and counterelectrodes). To detect that an adequate sample is present in the samplechamber and that the blood sample has traversed the reagent layer andmixed with the chemical constituents in the reagent layer, the meter mayapply a fill-detect voltage between the fill-detect electrodes andmeasures any resulting current flowing between the fill-detectelectrodes. If this resulting current reaches a sufficient level withina predetermined period of time, the meter indicates to the user thatadequate sample is present and has mixed with the reagent layer.

FIG. 1 illustrates a general cross-sectional view of an embodiment of atest strip 10 consistent with the present invention. Test strip 10 maycomprise a test strip as described in U.S. patent application Ser. No.11/181,778, incorporated herein by reference in its entirety. Test strip10 includes a proximal connecting end 12, a distal end 14, and is formedwith a base layer 16 extending along the entire length of test strip 10.Base layer 16 is preferably composed of an electrically insulatingmaterial and has a thickness sufficient to provide structural support totest strip 10. Disposed on base layer 16 is a conductive pattern (notshown).

The conductive pattern (not shown) includes a plurality of electrodesdisposed on base layer 16 near proximal end 12, a plurality ofelectrical strip contacts disposed on base layer 16 near distal end 14,and a plurality of conductive traces electrically connecting theelectrodes to the plurality of electrical strip contacts, the contactsbeing an area intended for mechanical engagement with anothercorresponding contact. In an embodiment consistent with the presentinvention, the plurality of electrodes may include a working electrode,a counter electrode, and fill-detect electrodes.

A dielectric insulating layer 18 may be formed over the conductivepattern along a portion of the test strip between the measuringelectrodes and the plurality of electrical strip contacts in order toprevent scratching, and other damage, to the electrical connection. Asseen in FIG. 1, the proximal end 12 of test strip 10 includes a samplereceiving location, such as a sample chamber 20 configured to receive auser's fluid sample. The sample chamber 20 may be formed in part througha slot formed between a cover 22 and the underlying measuring electrodesformed on base layer 16. The relative position of the measuringelectrodes and the electrical strip contacts form a proximal electroderegion 24 at one end of strip 10 and a distal strip contact region 26 atthe other end.

FIG. 2 illustrates a top perspective view of a test strip 10 insertedwithin a meter connector 30 consistent with the present invention. Teststrip 10 includes a proximal electrode region 24, which contains thesample chamber and measuring electrodes, as described above. Proximalelectrode region 24 may be formed to have a particular shape in order todistinguish to the user the end receiving a fluid sample from distalstrip contact region 26. Meter connector 30 includes channel 32extending out to a flared opening for receiving the test strip 10. Meterconnector 30 may further include tangs 36 extending a predeterminedheight above the base of channel 32. The predetermined height of tangs36 is selected to limit the extent, such as through a correspondingraised layer of test strip 10, to which a test strip 10 can be insertedinto channel 32.

Meter connector 30 further includes a first plurality of connectorcontacts 38, disposed closer to the proximal end of meter connector 30,and a second plurality of connector contacts 40 disposed closer to thedistal end of meter connector 30.

FIG. 3 illustrates a general cross-sectional view of a test stripinserted within meter connector 30 consistent with the presentinvention. Channel 32 depicts a proximal row of connectors comprising afirst plurality of connector contacts 38. In addition, channel 32 housesa distal row of connectors comprising a second plurality of connectorcontacts 40. First plurality of connector contacts 38 and secondplurality of connector contacts 40 make contact with distinct portionsof distal strip contact region 26.

Connector contacts may have either levels of high or low impedance,producing a code yielding a code index. In an embodiment consistent withthe present invention, the code is a binary code based on the number ofcontact pads (P) implemented, where the number (N) of codes is equal toN=2^(P). Although an embodiment consistent with the present inventionutilizes a binary code, other types of codes may be used consistent withthe present invention, and embodiments are not limited thereto.

However, another embodiment consistent with the present inventionincorporates an auto-on/wake-up feature, and the number of codespossible when integrated with an auto-on/wake-up feature, however, isreduced to N=2^(P)−1. In a system having an auto-on/wake-up feature, acode with all zeros (all high impedance) is not an active code as itwill not wake up the meter. The code, whether the possible number is2^(P) or 2^(P)−1, includes encoded test information, calibrationinformation, and information relating to error detection, rejection,minimization or correction. Because the number of possible codes islimited by the number of contact pads, it is important to use a methodof error detection, rejection, or correction which does not exhaust thepossible code space, and allows sufficient test and calibrationinformation to be encoded on test strip 10.

When test strip 10 is inserted into meter connector 30, one contact isclosed and wakes up the meter by pulling the microcontroller's interrupteither high or low. The meter will then check the voltage out (V_(out))to determine the test type and then read the code bits to determine thecode value. The code value selected can, for example, be associated witha stored set of coefficients in the meter's memory for use in a glucosemapping algorithm that is particularly correlated to the reagent appliedto the measuring electrode region. This code can also be associated withother types of strip parameter information, such as those referencedabove. It could also select different meter configuration options aswell. This can also be used to determine strip identification (checkstrip, manufacturing probe, and different test type). Furthermore, thecode can be indicative of an error detection, rejection, correctionroutine, method, or algorithm.

The incorporation of individualized code data within individual teststrips provides numerous advantages in addition to those associated withaccuracy of measurement. For example, with individual strip coding auser no longer needs to manually enter the meter's lot code, eliminatingthe possibility of user technique error for this critical step. Striplot codes stored directly on individual test strips will also provide ameans to ship mixed lots of strips in a single strip vial. In contrast,current technologies such as button/key coding require all strips(typically packaged in a vial including 50 strips from the same lot) ina vial to be from the same lot code.

FIG. 4 is a top view of a distal portion of test strip 10 illustratingdistal strip contact region 26, consistent with an embodiment of thepresent invention. The conductive pattern (not shown) formed on baselayer 16 extends along test strip 10 to include distal strip contactregion 26. Distal strip contact region 26 is divided to form distinctconductive regions 42 and 44. Conductive region 44 is divided into fourcolumns forming a first plurality of electrical strip contacts, labeled46, 48, 50, and 52 respectively. First plurality of electrical stripcontacts 46, 48, 50, and 52 are electrically connected to the pluralityof measuring electrodes at the distal end of the test strip 10. Itshould be understood that the number of the first plurality ofelectrical strip contacts 46, 48, 50, and 52 are merely exemplary, andthe system could include fewer or more electrical strip contactscorresponding to the number of measuring electrodes included in thesystem.

First plurality of electrical strip contacts 46, 48, 50, and 52 aredivided, for example, through breaks 54 formed through the underlyingconductive pattern (not shown) in test strip 10. An additional break 54divides conductive region 44 from conductive region 42 within distalstrip contact region 26, and a further break 54 separates the upperright-hand portion of distal strip contact region 26 to form a notchregion 56, as will be described more fully in detail below.

Conductive region 42 is divided into five distinct regions outlining asecond plurality of electrical strip contacts forming contacting pads58, 60, 62, 64, and 66. As noted above, the conductive pattern on baselayer 16 can be applied to the top side of the strip, the bottom side ofthe strip, or a combination of both. Contacting pads 58, 60, 62, 64, and66 are configured to be operatively connected to the second plurality ofconnector contacts 40 within meter connector 30. Through this operativeconnection, the meter is presented with, and reads from the contactingpads, a particular code representing information signaling the meter toaccess data related to test strip 10. The breaks 68 isolate an outermostdistal connecting end 70 of the distal strip contact region 26.

FIG. 5 illustrates meter connector 30 receiving distal strip contactregion 26 of test strip 10 consistent with the present invention. FIG. 5depicts first plurality of connector contacts 38, labeled 1-4respectively, and second plurality of connector contacts 40, labeled 5-9Connector contacts 38 and 40 make contact with distinct portions ofdistal strip contact region 26. In particular, upon proper insertion oftest strip 10 into connector 30, first plurality of electrical stripcontacts 46, 48, 50, and 52 are respectively electrically connected toconnector contacts 1-4, which form first plurality of connector contacts38. Similarly, contacting pads 58, 60, 62, 64, and 66, which form thesecond plurality of electrical strip contacts, are respectivelyelectrically connected to connector contacts 5-9, which form secondplurality of connector contacts 40.

In an embodiment consistent with the present invention, the connectionbetween contacting pad 66 and connector contact 9 establishes a commonconnection to ground (or a voltage source where the polarity isreversed), thereby completing an electric circuit, which includes themeter and at least a portion of conductive region 42. The completion ofthis circuit can perform a meter wake-up function, providing a signal tothe meter to power up from low-power sleep mode. Accordingly, connectorcontact 9 may be positioned proximally relative to the remainingcontacts 5-8, in order to ensure that contacts 5-8 are in properconnecting position prior to the final closing/wake-up of the circuitthrough the connection of contacting pad 66 and connector contact 9.Furthermore, because in another embodiment consistent with the presentinvention, a non-conductive insulating ink strip can be formed at thedistal end of the test strip 10 and also because a conducting substancecan be removed from notch region 56 (shown in FIG. 4), premature wake-upof the meter may be prevented.

That is, distal movement of test strip 10 within the connector channel32 does not establish a common connection at the point connector contact9 engages the extreme distal edge of test strip 10. Rather, a commonconnection will be established only when the connector contact passesnotch 56, and ink strip if applied, and engages a conductive portion ofcontacting pad 66, providing a reliable connection.

As noted above, contacting pads 58, 60, 62, 64, and 66 are configured tobe operatively connected to second plurality of connector contacts 40within meter connector 30. Through this operative connection, the meteris presented with, and reads from the contacting pads, a particular codesignaling the meter to access information related to test strip 10. Thecoded information may signal the meter to access data including, but notlimited to, parameters indicating the particular test to be performed,parameters indicating connection to a test probe, parameters indicatingconnection to a check strip, calibration coefficients, temperaturecorrection coefficients, ph level correction coefficients, hematocritcorrection data, and data for recognizing a particular test strip brand.In addition, the coded information may be indicative of a errordetection, rejection, or correction method.

FIG. 6 illustrates an test strip having a sample code embedded thereon,consistent with the present invention. As shown in FIG. 6, conductivecontacting pads 60 and 64 are overprinted with an electrical insultingmaterial, such as, for example, a non-conductive (insulating) ink layer75. Non-conductive ink layer 75 increases the impedance between thecorresponding connector contacts (in this example, connector contacts 6and 8) and the underlying strip portion at various predeterminedcontacting pads within the conductive region 42 of distal strip contactregion 26.

Upon connection of contacting pads 58, 60, 62, 64, and 66 tocorresponding connector contacts 40, the meter will read a particularcode based on the number, and pattern, of contacting pads overprintedwith non-conductive ink layer 75. That is, the use of non-conductive inklayer 75, provides a switching network to be read by the meter. When aninsulator is printed over one of the conductive surfaces of contactingpads 58, 60, 62, 64, and 66, it prevents the flow of electric currenttherealong and alters the conductive path between the contacting pad andconnector contact. When no insulator is printed over the conductorcurrent flow is relatively unimpeded.

Upon reading a particular code, an internal memory within the meter canaccess, through a stored microprocessor algorithm, specific calibrationinformation relating to the particular test strip, or an errordetection, rejection, or correction method, routine, or algorithm. Themeter can read the code through either an analog or digital method. Inthe analog mode, a preset resistive ladder is interconnected within themeter to the second plurality of connector contacts 40 (labeled 5-9 inFIG. 5) such that permutations of printed non-conductive ink can becorrelated to a distinct lot code using a voltage drop, resistance, orcurrent measurement. The analog method also can be simultaneously usedas the auto-on/wake-up feature as long as each code has at least one padfree of non-conductive ink that can make a low impedance connection towake the meter up by closing an open circuit. The analog voltage,resistance, or current level could be used to signal the meter to accessany of the data referenced above particular to test strip 10.

In a digital mode, as schematically represented in FIG. 7, eachcontacting pad 58-66, would be read as an individual input, unlike thesingle input used by the analog method. For the digital method to besimultaneously used as an auto-on/wake-up feature, the inputs would needto be wire-orred together or connected to an interrupt controller of amicro-controller. Each code must have at least one pad free ofnon-conductive ink 75 such that a low impedance connection can be madeto wake-up the meter's micro-controller.

Non-conductive ink 75 with levels of high and low impedance produce abinary code yielding a code index based on the number of pads (P)implemented, where the number of codes is N=2^(P). It is possible,however, for a code to comprise an arrangement where none of theelectrical strip contacts are covered with electrical insulatingmaterial (a code will all logical “1”s, i.e. all conductors). Asdiscussed above, the number of codes possible when integrated with anauto-on/wake-up feature, however, is reduced to N=2^(P)−1. In a systemhaving an auto-on/wake-up feature, a code with all zeros (allinsulators) is not an active code as it will not wake up the meter.

When test strip 10 is inserted into meter connector 30, one contact isclosed and wakes up the meter by pulling the microcontroller's interrupteither high or low. The meter will then check the voltage out (Vout) todetermine the test type and then read the code bits (S1, S2, S3, S4) todetermine the code value. The code value selected can, for example, beassociated with a stored set of coefficients in the meter's memory foruse in a glucose mapping algorithm that is particularly correlated tothe reagent applied to the measuring electrode region. In addition, thecode value selected can be associated with an error detection,rejection, or correction algorithm. The voltage drop across the seriesresistor R at Vout in FIG. 7 can be sensed, to determine if code valesare within a predetermined range for use as a confirmation signal. Thiscan also be used to determine strip identification (check strip,manufacturing probe, and different test type).

In addition to providing either a high or low impedance level (throughthe application or absence of an insulating layer of non-conductive ink75 over one of the contacting pads) a particular resistive element maybe applied over a particular contacting pad. The resistive elementintroduces an increased level of impedance into a circuit that reduces(but does not necessarily prevent) the flow of electric current.Accordingly, the use of a specific resistive element over a particularcontacting pad provides an intermediate level of resistance directly onthe contacting pad of the test strip. When this intermediate level ofresistance is connected to the meter through engagement with acorresponding meter connector contact, the meter can detect this“intermediate” level (e.g. through a circuit measurement of voltage dropby applying Ohm's and Kirchhoff's laws).

The detection of such an intermediate level can alert the meter'sprocessor to access an entire new set of code data relating to teststrip 10. In other words, providing a resistive element coating can beused to expand the number of codes available with a set number ofcontacting pads. For example, a strip may be formed with a particularcode through a particular pattern of non-conducting insulating ink 75.When one of the conducting contacting pads is formed to include aparticular resistive element, that same code represented by the patternof non-conducting ink 75 now can be read by the meter to access anentirely different set of data. As an example, the contacting pad 66 ofFIG. 6 (or any of the available contacting pads) could be formed toinclude a resistive element. As a non-limiting example, the resistiveelement could be provided in the form of a printed conductive ink. Thethickness of the printed ink forming the resistive element, andresistivity of the ink composition, can be varied to achieve the desiredresistance for a particular contacting pad. The additional informationmade available through this expansion of codes can include, but is notlimited to, information related to hematocrit correction, informationrelated to meter upgrades, information related to the particular striptype, or, as further discussed below, a checksum used in an errordetection and rejection algorithm. Accordingly, the use of such aresistive element can be used to expand the number of codeconfigurations available with a set number of contacting pads.

Consistent with an embodiment of the present invention, contacting pads58, 60, 62, 64, and 66 may be used to represent individual unit valuesof a code, and when taken in combination, form a code value. In oneembodiment, the contacting pads represent digital bits, which may beencoded in binary. That is, each of contacting pads 58, 60, 62, 64, and66 may represent a binary value of “1” or “0” in the code, such that ifcontacting pad 58 is assigned a binary value of 1, it is equal to2^(n−1), with n being the number of contacting pads. In the presentexample, contacting pad 58 would have a unit value of 2⁴ or 16, if thereis a digital “1” assigned to it, or 0, if there is a digital “0”assigned to it. Similarly, contacting pad 60 may have a unit value of 8or 0, contacting pad 62 may have a unit value of 4 or 0, contacting pad64 may have a unit value of 2 or 0, and contacting pad 66 may have aunit value of 1 or 0. Thus, a code of 01010 has individual unit valuesof 0, 8, 0, 2, 0, and a combined code value of 10.

Consistent with embodiments of the present invention, contacting pads58, 60, 62, and 64 may also have unit values other than theaforementioned digital bits. For example, contacting pads 58, 60, 62,and 64 may have unit values in the form of analog readings, symbols, orpictograms. Analog reading unit values may be related to actual readingsof properties associated with contacting pads 58, 60, 62, and 64, suchas the resistance, and the code value may be the combination of theindividual resistances.

Symbol or pictogram unit values may be in the form of lines, shapes,pictures, etc. For example, contacting pad 58 may have a unit value offour lines, contacting pad 60 may have a unit value of three lines, andso on, such that the code value is equal to the total number of lines.In another example, contacting pads 58, 60, 62, 64, and 66 may havedifferent shapes assigned to each pad, and the code value is the set ofshapes. Symbols or pictograms may also be used in conjunction withdigital bits and analog readings such that a digital “1” or “0”, or ananalog reading greater than or equal to a predetermined value enablesthe symbol or pictogram to be present on the contacting pad.

Contacting pads 58, 60, 62, 64, and 66 represent individual bits of theembedded code as discussed above, and as fully described in U.S. patentapplication Ser. No. 11/181,778, which is incorporated herein byreference in its entirety. As mentioned throughout this specification,consistent with an embodiment of the present invention, the embeddedcode may include information enabling an error detection or rejectionmethod. In one embodiment consistent with the present invention, theerror detection or rejection method uses a trending algorithm to detectand reject errors. For example, consider a vial containing fifty teststrips. If the meter reads a code which is different than the last coderead, and the number of the test strips used is less than fifty, themeter will indicate that there is a potential error. That is, consistentwith an embodiment of the present invention, a trending algorithm usesrecent and over-time trends as a basis for determining if a read codediffers enough from an expected value to qualify as an error.

FIG. 8 is a flowchart illustrating a method for performing errordetection and rejection using a trending algorithm, consistent with thepresent invention. First, test strip 10 is inserted into the meter, andread by the meter (S801). Next, a predetermined characteristic of thetest strip is recorded, and saved in the memory of the meter (S802). Thepredetermined characteristic of the test strip may be any performancemeasure, including lot code or other manufacturing information regardingthe test strip, or may be related to the property being measured by thetest strip. A trending analysis is then performed on the recordedcharacteristic to obtain an expected value (S803). The trending analysisanalyzes recorded characteristics from previously used test strips andthe present test strip to obtain an expected value. The trendinganalysis may include performing averaging over the set of read teststrips, or may include using a learning algorithm. Consistent withembodiments of the present invention, the learning algorithm maycomprise an auto-adaptive learning algorithm, and may also include userfeedback.

Returning to FIG. 8, the meter will then determine if the recordedcharacteristic of the present test strip differs from the calculatedexpected value (S804). If the recorded characteristic does not differfrom the calculated expected value, the meter will read and process theencoded data (S807), and may store the encoded data as a data point tobe included in the trending analysis. If the recorded characteristicdiffers from the calculated expected value, the meter will indicate aread error (S805), and the user may discard the test strip and obtain anew strip (S806). Alternatively, consistent with an embodiment of thepresent invention, if the recorded characteristic differs from thecalculated expected value, the meter will indicate a read error (S805),and may prompt the user for additional input (S808). For example,referring to the earlier example of a vial containing fifty strips,after indicating a read error, the meter may ask the user whether thetest strip is from a new vial, the lot code of the new vial, or maysimply request that the user to re-enter the strip into the meter forre-reading. Depending on the answer to the prompt, the meter may thenread and process the encoded data (S807), and then store the encodeddata as a data point to be included in the trending analysis.

In another embodiment consistent with the present invention, theembedded code may include information enabling an error detection orrejection method which uses a checksum, which may include computing amodulus of the bits of the code, to detect and/or reject errors. Inorder to perform a checksum, additional checksum bits are embedded ontest strip 10 along with the embedded code that is used to signal themeter to access any of the data referenced above particular to teststrip 10. When test strip 10 is inserted into the meter, a codeindicative of a checksum method is encoded thereon, and signals themeter to perform a checksum algorithm stored in a memory of the meter.In general, the meter executes an algorithm which determines the modulusof the calibration code, and compares it to an expected value. In aspecific embodiment consistent with the present invention, the checksummethod computes the modulus of the bits of the calibration code, andcompares it to the modulus value also encoded on test strip 10. The readcalibration code embedded on the test strip will be rejected if thecomputed modulus does not match the encoded modulus. The checksum bitsmay be encoded using a printed insulated pads, or by varying theresistance of the contact pads, as discussed above, or may be encoded bydepositing an optical marker on contacting pads 58, 60, 62, 64, and 66.In an embodiment consistent with the present invention, the checksumbits may be encoded using a different method than the calibration bits.By encoding the checksum bits using a method that is different from themethod used to encode the calibration bits, errors caused due tomanufacturing tolerances will not be duplicated between the checksum andcalibration bits, ensuring that the error will be rejected by virtue ofa checksum which does not match. In embodiments consistent with thepresent invention, the checksum bits may be base 2 or binary, or may bebased on other encoding methods. The checksum bits can also be encodedby known methods, such as using magnetic, or optical means (such as barcodes), notches cut into the substrate of test strip 10, and the like.

Consistent with an embodiment of the present invention, the checksumbits may be a parity bit, or single bit checksum, or may be a multiplebit checksum. A parity bit checksum allows for an error detection orrejection method which sacrifices only a single bit to detect an error.A parity bit checksum, however, will only protect against an odd numberof bit read errors allowing an even number of bit read errors to goundetected. A parity bit checksum provides for 100% rejection of singlebit errors and 50% detection and rejection for multi-bit errors. In anexample consistent with a present invention, for a test strip having abinary system employing P number of contact pads for encodinginformation, as discussed above, will result in N codes where N=2^(P).Utilizing a parity bit, the effective code space will be reduced to N/2or N=2^(P−1).

A multi-bit checksum is more robust than a parity bit checksum, butsacrifices more usable bits to accomplish the task. A multi-bit checksumprovides a greater level of error detection and rejection, detectingboth odd bit errors and some even bit errors. Using a multi-bitchecksum, however, will use a greater number of bits and may not detecterrors in bit order. Multi-bit checksums offer 100% rejection of singlebit errors and at least 75% rejection of multi-bit errors depending onthe number of bits for the checksum related to the calibration bits. Fora binary system employing C number of checksum bits where C<P, theeffective code space will be reduced to N=2^(P-C).

FIG. 9 is a flowchart illustrating a method for performing errordetection and rejection using a checksum algorithm which includescomputing a modulus of the bits in the code, consistent with the presentinvention, First, test strip 10 is inserted into the meter, and the codeembedded thereon is read by the meter (S901). The meter includes amemory which contains instructions for instructing the meter's processorto determine the modulus of the code and compare it with a specificvalue. Within the code embedded on test strip 10 there is also anembedded expected value of the modulus, which the meter reads and storesin the memory. The meter then determines the modulus of the bits in theembedded code (S902), and compares the modulus to the stored expectedvalue (S903). The meter determines if the expected value matches themodulus (S904). If the expected value and the modulus match, the meterwill proceed to read and process the encoded data on test strip 10indicative of any of the factors referenced above, including performinga test on a fluid sample, as specified by the information encoded ontest strip 10 (S905). If the modulus of the bits does not match theexpected value, the meter will indicate a read error (S906), and theuser should discard the test strip and obtain a new one (S907).

In another embodiment consistent with the present invention, a redundantcode may be encoded on test strip 10. Encoding test strip 10 with aredundant code enables the meter to detect and reject multiple bit readerrors. A code, which may be indicative of the lot of the test strip, orany other factors as referenced above, is first encoded on test strip10, and then the same, or redundant, code is again encoded on test strip10, and both codes must match in order for the code to not be rejectedby the meter. In an embodiment consistent with the present invention,the redundant iteration of the code is encoded in a different bitsequence than the original iteration of the code. When the original codeand the redundant code are encoded in a different bit sequence, thecodes are less susceptible to manufacturing location variation. Byaltering the bit sequence of the embedded codes variations due tophysical shift or machine offset will not be translated into identicalbit errors for both codes. This is advantageous, because, if theidentical bit error is present in all embedded codes the error will goundetected.

In another embodiment consistent with the present invention, instead ofencoding the redundant code in different bit sequence, the code may beencoded using different methods of manufacturing, or embedding the code,using a different method, such as, electrical, optical, or magnetic.Moreover, the use of a redundant code may further be combined with achecksum, as described above, for an increased level of error detectionand rejection.

FIG. 10 is a flowchart illustrating a method for performing errordetection and rejection using a redundant code, consistent with thepresent invention. First, test strip 10 is inserted into the meter, andthe first code is read by the meter (S1001), and then the second code,which is a redundant iteration of the code, is read (S1002). The meterthen determines if the first code matches the second code (S1003), Ifthe first code and the second code match, the meter will proceed to readand process the encoded data on test strip 10 indicative of any of thefactors referenced above, including performing a test on a fluid sample,as specified by the information encoded on test strip 10 (S1004). If thecode and the second code do not match, a user discards test strip 10,and obtains a new strip, and starts the process again (S1005).

Consistent with another embodiment of the present invention a codereduction method may be utilized to provide error detection andrejection. Where the checksum and redundant coding methods disclosedabove require exclusive bits which could otherwise be used for codingcalibration lot information, the type of test, etc., a code reductionscheme utilizes all bits for coding information. In this embodiment,certain bit combinations, or codes, are identified as being excludedfrom a predetermined set of acceptable or valid codes. The set of validcodes may be stored in a memory of the meter. This method allows for thedetection and rejection of multiple bit errors, and a possible level oferror detection and rejection that may be greater than that of using achecksum or a redundant code.

Selectively reducing the amount of valid codes may be based on anexclusion set that can have a number of members M, where M>0 and M<N,where N is the number of possible codes. The set selected for exclusionis chosen to arrive at an acceptable level of error detection andrejection, while retaining an acceptable number of available codes. Theset of codes selected for reduction, or the set of invalid codes, may berelated to the number of 1s or 0s in a code, or may be related to theevenness or oddness of the bits. The means for exclusion are not limitedto these example, but may be found to be easier to implement.

As an example, for a binary system employing P number of pads forencoding an error detection and rejection code will result in N codeswhere N=2^(P). By selectively reducing the number of valid codes by, forexample, eliminating values where the code has a count of 1s which isequal to Y, where Y≤P, the count of 1s (or 0s) are symmetric where thecount of zero 1s equals the count of P 1s and the count of two 1s equalsthe count of P−1 1s.

As another example, using a binary system where P=5 results in a codespace of N=32, and has a zero percent detection/rejection rate, i.e.,all codes are valid. By selectively excluding codes that have a valuecontaining two 1s, the possible number of codes is reduced by 10 to 22and results in a possible detection/rejection rate of 45.5%. Similarly,a lower level of protection can be selected by selectively excludingcodes that have a value containing one or zero 1s. Because there arefive possible codes which have one 1, and one possible code that haszero 1s, the code space is reduced by six to 26 possible codes, andresults in an error detection/rejection rate of 23%. That is, thepercentage of invalid codes, resulting from manufacturing defects, etc.,that will be detected and rejected by the meter, is 23%.

Consistent with the present invention, the above described methods ofselectively excluding codes is extended to the possible code values andunit values, as discussed above, For example, consider a four unit codecomprised of unit values in the set of {A, B, C, D}. The possible codevalues from this set would include {A, B, C, D}, {B, B, C, B, C, D}, {D,B, C, D}, {A, C, C, D}, and so on including all possible sequences anditerations of {A, B, C, D}. Due to known tolerances, certain codevalues, or certain unit values may have a higher propensity of havingerrors associated therewith. For example, the code value {D, D, A, C},or the unit value of a fourth position {A}, may be known to have a higherror rate, or a high probability of being misread as a different codevalue or unit value. Accordingly, a set of code values or unit valueswhich are likely to be erroneous could be generated as an exclusion set,or conversely a set of acceptable code values, such that unit values orcode values having a high error rate, or which generate serious errors,can be excluded. This method can be further applied to unit values suchas digital bits, analog readings, symbols, or pictograms, as describedabove.

FIG. 11 is a flowchart illustrating a method for performing errordetection and rejection using a method of selectively reducing thenumber of available code values, consistent with the present invention.This method may also be applied by selectively reducing certain unitvalues, as well. First, test strip 10 is inserted into the meter, andthe code embedded thereon is read by the meter (S1101). The metercompares the code value with a predetermined set of acceptable codevalues, which may be stored in the memory of the meter (S1102). Themeter determines if the code value on test strip 10 matches a code valuethat is on the predetermined set of acceptable code values (S1103). Thepredetermined set of acceptable code values, in one embodimentconsistent with the present invention, contains code values which havethe highest probability of not containing an error based on knownmanufacturing tolerances and conditions. If the code value on test strip10 matches a code value on the predetermined set of acceptable codevalues, the code value is determined to be a valid code, and the meterwill proceed to read and process the encoded data on test strip 10indicative of any of the factors referenced above, including performinga test on a fluid sample, as specified by the information encoded ontest strip 10 (S1104). If the code value does not match a code valuecontained on the predetermined set of acceptable code values, test strip10 likely contains manufacturing defects, the meter will indicate anerror and the user should discard the strip and obtain a new strip(S1105).

TABLE 1 Errors Error codes Code Bit 3 Bit 2 Bit 1 Bit 0 Bit 3 Bit 2 Bit1 Bit 0 0000 1000 0100 0010 0001 8 4 2 1 0001 1001 0101 0011 0000 9 5 30 0010 1010 0110 0000 0011 10 6 0 3 0011 1011 0111 0001 0010 11 7 1 20100 1100 0000 0110 0101 12 0 6 5 0101 1101 0001 0111 0100 13 1 7 4 01101110 0010 0100 0111 14 2 4 7 0111 1111 0011 0101 0110 15 3 5 6 1000 00001100 1010 1001 0 12 10 9 1001 0001 1101 1011 1000 1 13 11 8 1010 00101110 1000 1011 2 14 8 11 1011 0011 1111 1001 1010 3 15 9 10 1100 01001000 1110 1101 4 8 14 13 1101 0101 1001 1111 1100 5 9 15 12 1110 01101010 1100 1111 6 10 12 15 1111 0111 1011 1101 1110 7 11 13 14

In another embodiment consistent with the present invention, anarrangement method is used to minimize the impacts of possible biterrors. In situations where the utilization of a bit error detection andrejection scheme is less than optimal, limiting the impact of a biterror is an acceptable alternative. Bits embedded on test strip 10typically have different probabilities of being prone to an error. Thesediffering probabilities can be used to minimize the impact of a possiblebit error by constructing a logical arrangement placing the bits atdifferent locations than their actual physical locations to reduce theimpact of a bit error. Table 1, below, shows a 16 codes in a 4-bitbinary coding scheme, and the possible single bit errors. The erroneouscodes are determined by summing the bits wherein a 1 in the 3^(rd) bitequals 8, a 1 in the 2^(nd) bit equals 4, a 1 in the 1^(st) bit equals2, and a 1 in the 0^(th) bit equals 1.

As shown in Table 1 all possible binary codes have four possible singlebit errors. The results of Table 1 are further shown in Table 2,illustrated in FIG. 12. Table 2 shows the same results using an errorgrid. Table 2 shows just how close or far away from the expected code, asingle bit error will cause the read code to deviate. The verticalnumbers correspond to the intended (actual) code number, and thehorizontal numbers correspond to the actually read code numbers. Solidblack shading indicates the expected code, grid lines indicate the leastsignificant bit error, diagonal lines indicate the next significant biterror, horizontal lines indicate the next significant bit error, andvertical lines indicate the most significant bit error.

Due to manufacturing tolerances, and the likelihood of particular bitsbeing incorrect and causing an error, certain codes have higherprobabilities of having particular single bit errors, and certain singlebit errors will cause a read code to deviate more from the expected thanothers, as is illustrated in Table 2. By constructing a logicalarrangement of the codes with respect to the most significant bit errorand the least significant bit error, it can be minimized as to how far acode can stray from the expected, and still produce an acceptableresult. From this logical arrangement, the codes having a predeterminedprobability of acceptable bit errors may be used as a code space andaccepted, regardless of an error in the least significant bit, as theywill have a lesser effect on the magnitude of the measured property.

FIG. 13 is a flowchart for illustrating a method for constructing alogical arrangement consistent with an embodiment of the presentinvention. First, the probability of each bit in the code to beerroneous is determined (S1201). The probability may be due to, forexample, manufacturing tolerances. As an example, referring to teststrip 10 having contacting pads 58, 60, 62, 64, and 66, the bit encodedby pad 58 is likely to have the highest probability of having an errorbecause it is at an edge of the strip, wherein manufacturing processesare more likely to damage or misproduce contacting pad 58. Conversely,an interior pad, such as contacting pad 62, has the lowest probabilityof having an error. Accordingly, the bit having the highest probabilityof having an error is logically replaced by the bit having the lowestprobability of having an error (S1202). Next, in a similar process, thebit having the next highest probability of having an error is logicallyreplaced by the bit having the next lowest probability of having anerror, and so on, until all bits have been logically replaced (S1203).After all of the bits have been logically replaced, a logicalarrangement of the bits is constructed (S1204). The logical arrangementwould result in the bits being laid out in a sequence which is differentthan the sequence in which they appear on test strip 10. For example alogical arrangement of test strip 10 with contacting pads in thesequence of 58, 60, 62, 64, and 66, may appear as 62, 66, 58, 64, 60.

Moreover, the logical arrangement may be performed in two ways, asequential arrangement, wherein the logical bits are arranged to keepthe code in sequence, or a non-sequential arrangement, wherein theoriginal bits remain in sequence, but the resulting code space isarranged logically, based on the logical replacements. The logicalarrangement determines how the meter reads the actual code that isembedded on the test strip. That is, in a sequential arrangement, themeter will read the test strip as having the logical code arrangement,and in a non-sequential arrangement, the meter will read the test stripas having the actual code, but correlate the actual code to the logicalcode space which is created from the logical arrangement. Moreover, theresult of using the sequential or non-sequential arrangement methods iscreating a code space to be recognized by the meter as having acceptablecodes, such that a test strip having a code with the least significantbit errors will be acceptable, and having a code with the mostsignificant bit errors will not be acceptable.

Further consistent with an embodiment of the present invention, a methodfor performing an error correction may be used to correct codes thathave been rejected, or detected as having bit code errors. For example,consistent with the present invention, a Hamming code can effectively beused to correct errors since the number of bits encoded on the teststrips has a fixed length. Hamming codes are well known intelecommunications, and are used to protect against errors intransmitted digital data, or scanned data, such as magnetic stripe orbar code. A Hamming code typically uses additional error correction orerror check bits which are encoded along with the encoded information,such that the additional error correction/check bits are arranged suchthat different incorrect bits produce different error results, allowingfor the identification and correction of the bit error. Specifically, aHamming code includes three error check bits for every four bits ofencoded information, and can correct any single-bit error, and detectall single-bit and two-bit errors.

To include a Hamming code on test strip 10 consistent with the presentinvention, three error check bits would have to be added onto test strip10 for every four bits of information. The error check bits may beencoded onto test strip 10 using a printed insulated pads, or by varyingthe resistance of the contact pads, as discussed above, or may beencoded by depositing an optical marker on contacting pads 58, 60, 62,64, and 66. As an example, using test strip having contacting pads 58,60, 62, 64, and 66 as described above, with one contacting pad beingused to designate an auto-wake feature, test strip contains four usablepads, and four bits. By varying the resistance or depositing an opticalmarker on contacting pads 58, 60, 62, 64, and 66, three extra errorcheck bits can be encoded on to use a Hamming code.

Moreover, the above methods are not necessarily exclusive, and can beused in combination to provide a greater level of error detection andrejection than a single method alone. For example, the use of a checksumcan be combined with the reduced code set. Moreover, a modulus orchecksum may be used in combination with a Hamming code, enabling thedetection of a bit error at a higher level than either method alone, andthe subsequent correction of the bit error.

Although a Hamming code is well known and has been used to correctdynamically transmitted codes, a Hamming code has not been used tocorrect a statically read code, such as the code consistent with thepresent invention. Moreover, because the bits encoded on the test stripsof the present invention are statically read and cannot be retransmittedupon error detection, error correction such as by using a Hamming codemay be beneficial in saving the user time and money, by not having todiscard test strip 10 on the detection of an error, Combining themethods discussed above, e.g., such as a modulus with a reduced code setis also possible.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A method for minimizing the impact of potentialerrors that may occur when a device receives a first code comprising aplurality of bits arranged in a physical arrangement and beingassociated with a diagnostic test strip, the method comprising:determining a probability of each bit to cause a read error; andconstructing a logical arrangement of the bits different than thephysical arrangement based on the probability, wherein the logicalarrangement comprises the bits arranged such that the impact ofpotential read errors is minimized.
 2. The method according to claim 1,wherein the logical arrangement comprises the bits arranged such thatthe bit having the highest probability of causing a read error islogically replaced by the bit having the lowest probability of causing aread error, and the bit having the lowest probability of causing a readerror is logically replaced by the bit having the highest probability ofcausing a read error.
 3. The method according to claim 2, wherein thelogical arrangement results in a second code which is read in sequence.4. The method according to claim 2, wherein the logical arrangementresults in a second code which is not read in sequence.
 5. The methodaccording to claim 1 further comprising performing an error detectionand rejection algorithm on the logically arranged code and determiningthe constituent level of the fluid if the error detection and rejectionalgorithm detects an acceptable error or does not detect an error in thelogically arranged code.
 6. The method according to claim 1, wherein thelogical arrangement is performed as a sequential arrangement such thatthe logical bits are arranged to keep the code in sequence.
 7. Themethod according to claim 6, wherein the device reads the test strip ashaving the logical code arrangement in a sequential arrangement.
 8. Themethod according to claim 6, wherein the result of using the sequentialarrangement creates a code space to be recognized by the device ashaving acceptable codes, such that a test strip having a code with leastsignificant bit errors will be acceptable, and having a code with themost significant bit errors will not be acceptable to the device.
 9. Themethod according to claim 1, wherein the logical arrangement isperformed as a non-sequential arrangement such that the original bitsremain in sequence, but the resulting code space is arranged logically,based on the logical replacements.
 10. The method according to claim 9,wherein the device reads the test strip as having the actual code, butcorrelate the actual code to the logical code space which is createdfrom the logical arrangement in a non-sequential arrangement.
 11. Themethod according to claim 9, wherein the result of using thenon-sequential arrangement creates a code space to be recognized by thedevice as having acceptable codes, such that a test strip having a codewith least significant bit errors will be acceptable, and having a codewith the most significant bit errors will not be acceptable to thedevice.
 12. The method according to claim 1, wherein the device readsthe first code from the diagnostic test strip.
 13. The method accordingto claim 1, further comprising reading the first code associated withthe diagnostic test strip.